1. Field of the Invention
This invention relates to a light receiving member such as an electrophotographic photosensitive member, more particularly to a light receiving member suitable for an electrophotographic printer of the system in which a laser beam is subjected to imagewise line scanning, especially an electrophotographic photosensitive member for laser printer.
2. Description of the Prior Art
Heretofore, the laser beam which has been employed for an electrophotographic printer of the system by line scanning of laser beam was a gas laser with relatively shorter wavelength such as helium-cadmium laser, argon laser or helium-neon laser, and the electrophotographic photosensitive member used therefor was a CdS-binder type photosensitive layer having a large thickness or a charge transfer complex (IBM Journal of the Research and Development, January, 1971, P. 75-89). Accordingly, no multiple reflection of laser beam occurred within the photosensitive layer and hence no image of interference fringe pattern appeared practically during image formation.
Whereas, for the purpose of minituarization and designing at low cost of the device, a semiconductor laser has been utilized in recent years in place of the gas laser as mentioned above. Such a semiconductor laser, which has generally an oscillated wavelength in the longer wavelength region of 750 nm or higher, requires an electrophotographic photosensitive member having high sensitivity characteristic in the longer wavelength region, and electrophotographic photosensitive members for this purpose have been developed.
As the photosensitive member having sensitivity to the longer wavelength light (e.g. 600 nm or longer) known in the art, there may be included, for example, a lamination type electrophotographic photosensitive member having a laminated structure of a charge generation layer containing a phthalocyanine pigment such as copper phthalocyanine, aluminum chloride phthalocyanine, etc. and a charge transport layer, or electrophotographic photosensitive member using a selenium-tellurium film.
When such a photosensitive member having sensitivity to the longer wavelength light is mounted on an electrophotographic printer of the laser beam scanning system and subjected to laser beam exposure, an interference fringe pattern appears in the toner image formed, thus having a drawback that no good reproduced image can be formed. One of the reasons conceivable may be due to incomplete absorption of the laser with longer wavelength, which gives rise to right reflection of the transmitted light against the substrate surface and results in generation of multiple reflected light of the laser beam, with the result that interference occurs between such multiple reflected light and the reflected light on the surface of the photosensitive layer.
As the method for cancelling this drawback, it has heretofore been proposed to cancel multiple reflection occurring within the photosensitive layer by way of roughening of the surface of an electroconductive substrate employed in an electrophotographic photosensitive member according to the anodic oxidation method or the sant blast method, or providing a light-absorptive layer or a reflection preventive layer between the photosensitive layer and the substrate. However, no such method could cancel completely the interference fringe pattern appearing as a practical problem during image formation. Particularly, in the method wherein the surface of the electroconductive substrate is roughened, it is required to have an average surface roughness with a sufficient size in order to cancel the interference fringe pattern which appears during image formation. Whereas, according to the sand blast method, the maximum surface roughness will be increased as the average surface roughness is increased, and there is also a tendency that the amount of greater roughness is increased in the distribution of its roughness. For this reason, the portion with greater roughness will function as the portion for injecting carriers into the photosensitive layer, thus causing undesirable formation of white dots (black dots when employing a reversal developing system). Moreover, in the case of a great average surface roughness, it is difficult to produce electroconductive substrates having a roughened surface within a permissible range of average surface roughness with good yield in the same lot in manufacturing, and there remain a number of points to be improved. Also, in the method employing a light-absorptive layer or a reflection preventive layer, the interference fringe pattern cannot sufficiently be cancelled, and yet there is also involved the drawback that the manufacturing cost is increased.